PROBLEM TO BE SOLVED: To obtain a decoloring agent composition having reduced irritating odor and capable of imparting sufficient brightness to the hair, and further to obtain a hair dye composition. SOLUTION: The decoloring agent composition used by being mixed with an oxidizing agent comprises (a) at least one of ammonia and an ammonium salt, (b) 2.5-6.0 wt.% monoethanolamine, (c) 1.5-10.0 wt.% single nonionic surfactant, or 1.5-10.0 wt.% surfactants consisting of the 1.5-10.0 wt.% nonionic surfactant and <=1.5 wt.% cationic surfactant, and (d) water. The content of the component (a) is 0.08-0.78 wt.% expressed in terms of ammonia. The hair dye composition contains a hair dye besides the composition. The decoloring agent composition and the hair dye composition can be formed into oil-in-water type emulsions respectively by being formulated with higher alcohols and oil components, and can contain each a liquid crystal structure.
